I have been enthusiastic about astronomy since the Apollo years. A night under the stars re-energizes my spirit and leaves me refreshed. I particularly enjoy being out at dusk as fading twilight slowly reveals each starry visitor one by one and I wait with anticipation the night's search into the blackness of space. However, as the safari comes to an end with heavy eyes desiring rest, the last thing I want to do is haul scope, tripod, charts, eyepieces, etc. back indoors until the next excursion. I tried that for years before seeking relief through a backyard observatory. The Factors
The observatory described here is the second I have built (having moved in 1996) and I have found that each observatory design is governed by two important sets of factors: the site demands and the observing preferences. Knowing my site and observing habits will explain a lot about the design I chose.
First of all, there were three elements that my site presented:
Floor Design To keep costs down and to save my back, I decided against a concrete pad, especially on a hill accessible only by foot. Instead, I chose "post and beam" construction for the foundation and floor. Though each post would require a footing of concrete, these could be done with ready-mix concrete bags, hauled up and mixed in a wheelbarrow on site. Each footing was set below the frost line, which for my northern climate is 42". On top of this went a 12' X 8' floor made of 2" X 10" beams and 2" X 8" floor joists. This provides enough space for a couple of scopes, computer cabinet, a shelf for charts and one observer (occasionally someone will join me, but mostly I observe alone). This part was straight forward as Fig.1 shows. |
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However to prevent a gangly tripod from swallowing up the limited floor space, a 6" stainless steel pier was embedded in and filled with concrete. The floor was then framed around this leaving a 1" gap. This prevents foot traffic from causing the floor to come in contact with the pier and thus transferring unwanted vibration to the scope. Here is where planning was important. Two factors will affect the location of the pier: the type of scope and the height of the observer. I wanted the scope to be as far forward as possible to reveal the most sky, at a comfortable height for observing and at the same time, allowing the front roof section to close without hitting the scope. This took a lot of careful measuring and sketching on paper, long before actual construction began. For my needs these measurements ended up being 24" between the front wall and pier, and 15" from the floor to the top of the pier. The scope has to be positioned pointing north before the roof is closed. |
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Walls & Roof Access to the sky is done by opening and closing the roofs. To accomplish this I attached both roof sections to the wall using four stainless steel hinges. I used heavy-duty hinges, the kind used on commercial grade steel doors. One is placed near each |
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end of the wall with the two remaining, evenly spaced between. This more than supports each section, even with metal roofing applied. I used metal roofing to relieve snow in the winter. With an average of 150" of snow falling each year, the accumulated weight will cause a metal roof to periodically shed it's load (beats shoveling). The rear wall is 7' and the front a mere 2'. The side wall peak is 8' and centered along the wall. This results in a rear roof slope of 11deg. and a front roof slope of 67deg. The beam that supports the rear wall roof joists, is attached to the joists and rests on angle brackets on each side wall. This beam raises up and down with the rear roof and therefore is out of the way for viewing. Fig. 2 shows the pin that is screwed into the beam and drops into the side angles when the roof is lowered. This ties the side walls and beam together when the observatory is closed. The front roof section leans against this beam and is sealed by a stripped of foam it's entire length. A man-door (not shown) was framed into the rear half of the side wall. |
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Operation The opening and closing of the observatory is pretty straight forward. The front roof section is pushed open and then lowered with a hand-held rope until two more side ropes stop it at a position about 15deg. above horizontal. The rear roof section is then raised until stopped by side chains at about 56deg. above horizontal. This operation would be easy on the moon, where gravity and the resulting weight it gives to objects is about 1/6 of the earth's. But here on terra firma the task is not without effort. To make the conditions similar to those on our neighbor, I added counterweights to ease the load. Fig. 3 shows the 42 lb. weight that is attached to the rear roof section via a 4X4 mast and pulley. This arrangement allows the opening and closing to be accomplished with one hand. The chains are a safety precaution, preventing the roof from |
| being opened too far in the dark. Also the front roof section being nearly vertical can be easily pushed open and lowered with just one hand. At a point, about 50deg. from verticle, ropes attached to two 35 lb. weights (one along each side wall) stop the downward motion. This is also at a point where gravity would start to cause much more back-strain. On some nights of observing this is far enough; especially for the moon and planets. But when targets are near the horizon and lower field of view is necessary, then by lifting up lightly on just one weight the roof can be lowered an additional 25degrees. When closing the observatory these weights then assist in raising the wall the first 25 degrees, with the rest of the way easily accomplished unassisted, by pulling on the hand rope. |  |
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Comforts To make observing easier, I added electricity for such things as red lighting, a computer with electronic star charts, a video monitor for CCD imaging and three 12v. power- supplies for drives, CCD camera and dew shield heater. And there you have it – Lookum Observatory. Now when my observations for the evening are complete, all that's left to do is close the roof and go to bed. |
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Questions or comments welcomed by P.J. Anway at:
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